As such, retinal vascular occlusive diseases represent a major cause of visual impairment and blindness. The prevalence of the disease is between 0.7 and 1.6%. Compression of the retinal veins at arterio-venous (AV) crossings plays an important role in the development of branch retinal vein occlusion (BRVO). The mechanical narrowing of the vessel lumen is supposed to be the mechanism behind this fact. The present study should elucidate how BRVO influences retinal blood flow at retinal vessel crossings in comparison to healthy control subjects. Retinal blood flow at retinal bifurcations will also be assessed. In addition, a fundus image will be taken to assess retinal oxygen saturation.